Hi; I’m not Jewish, but I am involved in a project to build a tropical greenhouse in my area (Iceland). While the primary cultivation is designed to be exotic edible fruit, I thought it might be nice to also cultivate plants of religious significance to people, which may otherwise be hard to come by. Concerning Judaism, the four species immediately comes to mind. At the same time, keeping cultivation multiuse and of an interest to a wider market is important. Lulav: will any date palm (Phoenix dactylifera) suffice, or are the requirements more specific as to the variety? Are there any specific cultivation requirements? Etrog: I’m not quite clear on the grafting rules. For example, if one took a kosher citron and grafted on another variety (such as Buddha's hand, valued among certain Buddhist groups), would the citron growing on non-grafted branches still be kosher (genetically identical to the rootstock)? Or does having a graft anywhere on the tree "contaminate" the rest? Hadasim: Is any common myrtle (myrtus communis) sufficient? Any specific requirements? Aravot: many willow species grow here already, including ones that love to grow by rivers. Is it possible to know whether any of them are suitable? We have S. caprea, S. alaxensis, S. myrsinifolia, S. phylicifolia, S. lanata, S. herbacea, and S. arctica. Others are also possible to grow outside, where space isn’t as expensive. Are there any cold-weather Salix that are workable, or is there only a specific species that is kosher? Thanks!
Lulav: The verse says "Palm fronds". Every palm resembling a date palm (Phoenix dactylifera) is kosher. Canary palm is highly controversial and therefore not recommended. Etrog: Any grafting by an Etrog invalidates it completely. According to Jewish law, it is not considered an Etrog if it is grafted with other species. In order to grow citrons for the four species there is a need for expert farmers who will know how to reach the right result. In addition, there is a need for the supervision of a recognized Kashrut organization to certify that the citrons have a tradition that they are not grafted nor originate from a grafted tree and that everything is done properly with accordance to Jewish law. Without this, there will be no buyers for citrons. Hadassim: It is the myrtle, where the leaves cover the trunk, and every three or more leaves must be level to each other in one circle, no one lower than the other. Therefore, it is recommended to inquire with growers of Hadassim on what species are most suitable for growing Hadassim and which conditions are best for it. Aravot: There are different species of willows. There are three signs for an Arava which is kosher for the four species. 1. A red stem (or green, because when the sun shines on it, it becomes red). 2. A long and narrow leaf. 3. The leaf is smooth without serrated edges or with very slightly serrated edges. Most of the willows which have these signs grow aside a stream, but even if they grow elsewhere they are kosher as long as they have the three signs.